Variable Temperature Cooking Method and Apparatus

ABSTRACT

The present invention deals with a variable temperature cooking method that uses a predetermined variable temperature reference profile and adapts it by mapping its datapoints to actual cooking conditions entered by the user or modified based on the readings from an internal food temperature probe. It is shown that, in order to achieve more uniform through-the-thickness doneness of foods, a continuously decreasing temperature setting from a higher initial temperature to a lower final temperature consistently performs better than applying a constant temperature or a two-step temperature profile. Use of a probe for monitoring internal food temperature enables a predictive estimate of cooking duration based on cooking score or temperature which is used to modify an initially inaccurate cooking duration.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent No. 61/627,044 filed Sep. 17, 2011, which is herein incorporated in full for all purposes.

STATEMENT OF GOVERNMENT SUPPORT

None.

FIELD OF THE INVENTION

This invention is related methods and apparatus for variable temperature cooking.

BACKGROUND

During the days of the wood stoves, trying to hold a constant oven temperature was a challenge. When new combustion material was added, the fire would intensify and temperature would rise, and then when the combustion material was burnt out, the temperature would decrease. Before thermostat-controlled appliances were introduced, gas or electric ranges had continuous heating with the amount of heat controlled by a dial knob which made achieving the right temperature difficult and often required adjustments during the cooking period. Today, most ovens are able to hold a constant oven temperature, but is this really the optimum?

It is difficult to achieve uniform doneness when cooking thick pieces of food. Because heating occurs more quickly on the outside surfaces than on the inside, a temperature differential arises between the outer layers and the center, which results in a difference in doneness. For the center to achieve full doneness, the outer layers are usually overcooked. Overcooking means a dryer food with a less satisfactory taste. On the other hand, avoiding overcooking the outer areas can mean leaving the center area raw, which is equally undesirable to some palates.

The problem of assuring uniform cooking throughout the thickness has not been satisfactorily addressed. Slow cooking provides a way to achieve through-thickness uniform cooking because it provides sufficient time for the heat to penetrate inside the food. This enables cooking at almost constant temperature of the entire meat. An example of such a cooking technique is Hawaiian pig which is cooked at 300° F. or 275° F. or even lower temperatures instead of the normally recommended 350° F. Since, due to the long cooking time, the food has the tendency to dry out, special measures, like wrapping the food in leaves or foil, are needed to retain the moisture. The duration of such a cooking process is, in many instances, not practical and many prefer faster cooking methods even though the results may not be just as good.

A slow cooking method that takes advantage of some modern technologies is illustrated in U.S. Pat. No. 7,750,272. Besides the inherent long duration of the slow cooking process and food handling associated (i.e., wrapping), this method requires a temperature probe to be inserted inside the meat to continuously monitor internal temperature. The oven temperature is controlled based on the difference between a reference temperature and the internal temperature of the food. However, the choice of the internal temperature as a control parameter, even though might seem a good choice at first, is questionable due to the long time it takes to any changes in the oven temperature to propagate to the interior of the food. There is a significant delay before changes in the oven temperature affect the inside food temperature. Moreover, requiring an internal food probe limit ones choices as it adds complexity to the oven construction and its operation that a manufacturer or user may not want.

U.S. Pat. No. 3,259,056 teaches analog circuitry for controlling cooking time with a probe inserted into the meat, where the cooking cycle start is delayed so that the cycle ends immediately prior to the selected serving time. Oven temperature starts very high and gradually decreases to a holding temperature. Thermistor resistance of the internal probe is compared and the resultant voltage will increase or decrease oven temperature by use of a thermostat.

Another method of controlling the oven temperature based on feedback from a temperature probe inserted in the food is presented in U.S. Pat. No. 4,301,509. Here, the goal is to obtain a certain degree of doneness in exactly a pre-selected amount of time. Again, the long response time of the internal food temperature to changes in oven temperature makes this method imprecise. Also, the goal of ending the cooking at a precise time, even though an aspect of understandable convenience, puts culinary satisfactions like taste, flavors, and possible texture on a secondary importance level. Use of an insertable temperature probe is associated with reliability issues and adds a level of complexity that can increase cost and make oven operation more difficult.

Internal food probes are known in the art. However, other temperature controlled cooking methods have tried to base oven temperature on an instantaneous internal temperature reading rather than a cooking history. Those methods have important shortcomings. One problem is that doneness is highly dependent on the entire internal temperature history of the cooking process up to the time of measurement as well as its projection all the way to the end of cooking. Another aspect is the significant delay by which changes in the oven temperature affect internal temperature. None of these methods took into consideration through the thickness doneness uniformity which is specifically addressed here.

Therefore, improvements are needed, particularly for achieving a more uniform through-the-thickness doneness. It has been found here that it is more efficient to be able to refine an optimum cooking process by doing laboratory experiments in which specialized equipment and professional expertise is available, and then adapt the resultant variable temperature reference profiles to real cooking situations.

SUMMARY

Disclosed is an apparatus and method for variable temperature cooking in order to achieve improved cooking results as, for example, a more uniform through-the-thickness doneness of foods. For example, it is shown that, in comparison to a constant temperature or a two-step temperature profile, consistently better results are obtained by heating to a peak temperature and then reducing the temperature according to a progressively decreasing temperature profile. The apparatus includes programmable instructions and circuitry for controlling temperature according to a setpoint profile of time versus temperature stored in memory.

Various heating profiles can be tested experimentally for a certain food type and quantity and the results can be evaluated. The evaluation can be done by personally inspecting the food or by certified taste experts, or it can involve more scientific measurements. To assess through-the-thickness doneness, the internal food temperature can be continuously measured at different depths during cooking. The temperature histories are converted to doneness using a cumulative parameter called “cooking score”. Evenness of cooking score throughout the food can then be compared for each of the different setpoint temperature profiles.

One or more profiles can then be stored as preferred variable temperature reference profiles. A variable temperature reference profile is in general associated with a certain food type and can be characterized by a starting temperature, a final temperature, and a duration of cooking. A practical cooking situation differs in general from the reference configuration by one or more parameters like food quantity, initial setpoint temperature, cooking duration, doneness, and oven characteristics. To account for these variations, the cook can usually make a fairly accurate estimate of the additional time necessary for cooking and can enter it using a dedicated user interface. The cook can also decide to make changes to the starting and ending temperatures. In order to obtain results that resemble those of a preferred experiment, the corresponding reference temperature profile can be adapted to the practical situation, for example, by changing the cooking time to match an extended cooking duration or/and by changing the starting or ending temperatures. This is referred to as “stretching or compressing the variable temperature reference profile in the time domain” or “stretching or compressing the variable temperature reference profile in the temperature domain,” respectively. In practice, both temperature and time may be stretched by a mathematical transformation which is done as part of the variable temperature cooking algorithm. The transformation process may also be termed “a mapping process,” and will be described in more detail below.

In preferred embodiments, a sigmoid temperature setpoint profile and a median between a sigmoid and a parabolic temperature setpoint profile are shown to cook meat more evenly throughout its thickness, avoiding an overcooked skin or an undercooked center. Surprisingly, with the selection of one of these temperature profiles, the temperature in the center of the meat can cross over the temperature of the exterior, in other words it is possible that the center of the dish will cook faster than the exterior at certain points in the cooking cycle. The fact that the cooking rate at the center actually surpasses that on the exterior is an indication that a more uniform doneness distribution will be achieved. A linear temperature ramp from hot to warm over time also provides good results.

If, for example, the food quantity is substantially different, either larger or smaller than the quantities that are normally used, the cook's estimate of the cooking duration might be in error, and can negatively impact the final result. In such cases or just for convenience, an internal temperature probe such as normally used for measuring food temperature to assess the end of cooking can be used to adjust the variable temperature reference profile to match the changing cooking conditions. Based on the probe readings, the time required to reach the cooking criterion for temperature or cooking score can be projected using algorithms to better estimate the needed cooking duration. The oven computer can then perform the mathematical operations that “stretch” the reference temperature profile to match the new cooking duration for the food item. This shows that using a probe can help to more accurately adapt a variable temperature reference profile to less known cooking conditions. In selected embodiments, the probe-enabled oven is capable of variable temperature cooking sessions without any user intervention at all beyond selecting certain default conditions.

However, having a probe available is not an absolute requirement in order to take advantage of the benefits of variable temperature cooking and in some embodiments, the use of a variable temperature reference profile alone can relieve the need for a probe, simplifying the process and the electronics.

These improvements are applicable to the cooking of meat such as pot roasts, roasted turkey, pork loin, steak and so forth, and also to the cooking of bread, casseroles, pies, and other solid foods. Adaptations of the method may be used for leavening bread.

The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings, in which preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration and description only and are not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention are more readily understood by considering the drawings, in which:

FIG. 1 is a schematic depicting circuit elements of a variable temperature oven.

FIG. 2 is a block diagram depicting an embodiment of a program for variable temperature cooking.

FIG. 3 is a view of a first control interface for a variable temperature cooking apparatus.

FIG. 4 is a view of a second control interface for a variable temperature oven.

FIG. 5 depicts exemplary temperature profiles for variable temperature cooking.

FIGS. 6A-6B show cooking results obtained with a constant temperature heating profile of Example 1.

FIGS. 7A-7B show cooking results obtained with a constant temperature heating profile of Example 2.

FIGS. 8A-8C show cooking results obtained with a conventional two-step temperature heating profile of Example 3.

FIGS. 9A-9C show cooking results obtained with a sawtooth variable temperature heating profile of Example 4.

FIGS. 10A-10C show cooking results obtained with a sawtooth variable temperature heating profile of Example 5.

FIGS. 11A-11C show cooking results obtained with sigmoid variable temperature heating profile of Example 6.

FIGS. 12A-12C show cooking results obtained with a sigmoid variable temperature heating profile of Example 7.

FIGS. 13A-13C show cooking results obtained with a “median” variable temperature heating profile of Example 8.

FIG. 14 is a table summarizing experimental data from Examples 1-8.

FIG. 15 shows a time-stretched setpoint curve or profile.

FIG. 16 shows a temperature-stretched setpoint curve or profile.

FIG. 17 describes use of a target cooking score during a cooking cycle.

FIG. 18 describes use of a target probe temperature during a cooking cycle.

FIG. 19 describes methods for adjustment of oven temperature setpoint on the fly.

The drawing figures are not necessarily to scale. Certain features or components herein may be shown in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The drawing figures are hereby made part of the specification, written description and teachings disclosed herein.

NOTATION AND NOMENCLATURE

Certain terms throughout the following description are used to refer to particular features, steps or components of the invention, and may be used as terms of description and not of limitation. As one skilled in the art will appreciate, different persons may refer to the same feature, step or component by different names. Components, steps or features that differ in name but not in function or action are considered equivalent and not distinguishable, and may be substituted herein without departure from the invention. Certain meanings are defined here as intended by the inventor, i.e., they are intrinsic meanings. Other words and phrases used here take their meaning as consistent with usage as would be apparent to one skilled in the relevant arts.

“Microprocessor” or simply “processor”, refers to a device that accepts information in digital or similar form and manipulates it for a specific result according to a sequence of instructions which are stored in firmware or in non-volatile memory accessible by the microprocessor.

“Temperature controller” is a controller used for adjusting and maintaining a certain temperature in a cooking area according to received temperature setpoint information. In case of an oven cooking area, a temperature controller can be a thermostat that involves a temperature sensor. In case of a cooktop cooking area, a temperature controller can be a potentiometer controlling the amount of energy delivered to the heating element thus being able to raise or reduce its temperature.

“Cooking rate” (C_(R)) is a measure of the rate at which a food chemically transforms to achieve doneness at a certain temperature as described in co-owned US Pat. Publ. No. 2012/0100269, which is incorporated in full herein by reference.

“Cooking Score (CS)” refers to a measure of food doneness also as described in US Pat. Publ. No. 2012/0100269. Determining cooking score requires monitoring temperature as a function of time during cooking and represents the time integral of the cooking rate. It can be viewed as a measure of the extent to which the chemical reactions characteristic of the cooking process have proceeded at a certain time. The cooking score is measured in “cooking score units” (CSU) and has a numerical value. Doneness, on the other hand, represents an estimate by a food taster of the degree to which a food was cooked. The units can also be different. Doneness can take percentage values like 85%, 100%, or 115% which is the numerical representation of such qualitative values like “medium”, “rare”, or “well done”. Even though they are determined differently there is a very close relation between them. The relation between cooking score and doneness is usually scaled as part of the cooking score calibration process. For example, a cooking score of 120 CSU may represent a “medium” done food whereas a cooking score of 135 CSU may represent a “well done” food.

“Evenness Ratio” is a ratio between a cooking score at a first location versus the cooking score at a second location. In general, the Evenness Ratio represents the ratio between the cooking score at the top and the cooking score at the center, but may also be useful when describing the ratio of the cooking score near the bottom over the cooking score at the center of the food.

Calculation of cooking score allows experimental comparison of the uniformity of doneness achieved under different conditions, where the comparison is being made between different layers or surfaces of a food item such as a top surface versus a center of a pork loin, pot roast, turkey, loaf of bread. A more uniform through-the-thickness ratio is achieved when the Evenness Ratio approaches 1.0.

“Temperature history”—refers to the food temperature exposure over the cooking time. In general it starts when heating is initiated and ends when the heat is interrupted and the food is removed from the stove but can also extend to capture some of the cooling or keep warm period.

“Variable temperature reference profiles” are setpoint temperature histories stored in non-volatile memory which are usually determined experimentally for certain cooking condition like, for example, a certain food quantity, certain starting and ending temperatures, and so forth, in order to maximize certain cooking results like, for example, through-the-thickness doneness uniformity. A variable temperature reference profile, however, can also be entered by the user or downloaded from external media and can be retained in memory.

Variable temperature reference profiles, also called simply a reference profile or curve, are characterized by a complexity of setpoint temperature variation that a user would not realistically be able to adjust the temperature manually. Examples are a linear temperature variation, a parabolic temperature variation, a multistep temperature variation where there is more than one required adjustment to the temperature (two-step temperature profile), and a sigmoid temperature variation. The profiles are generally characterized by at least one region of smoothly varying temperature setpoints that descend from a higher initial setpoint to a lower ending setpoint. In one embodiment, the variable temperature reference profile is a set of datapairs (t,T) defining a starting temperature setpoint, an ending temperature setpoint, and a plurality of intermediate temperature setpoints that progressively decrease from the starting temperature to the ending temperature during said cooking duration.

“Applied variable temperature profile” refers to the setpoint temperatures values as a function of time which are used during a cooking process to control the oven temperature. At the start of cooking, the oven system defines an ‘initial’ setpoint applied variable temperature profile based on user input and stored variable temperature reference profiles. Input from a sensor, such as a temperature probe may be used to modify the setpoint temperature profile on the fly during a cooking cycle. Setpoint relates to the internal temperature of the oven, not the internal temperature of the food.

The applied variable temperature profile is obtained from a variable temperature reference profile modified by a mapping function. The mapping function is usually designed to retain as many of the characteristics of the reference temperature profile so that the benefits in cooking results are best preserved. The applied temperature setpoint may be stored, for example, in volatile memory such as RAM, whereas the reference temperature profile may be stored in non-volatile memory such as ROM or EEPROM, while not limited thereto.

“Cooking area” is the area where a food is placed for being exposed to heat during cooking. It is understood for this invention that a cooking area represents an area like in most domestic heating appliances where the food does not undergo any significant displacements during cooking but it may be allowed to rotate.

“Monitoring parameter” is a parameter derived from the internal food temperature provided by a probe on which the monitoring of the cooking process is based on. It can be either temperature or, more generally, a cooking score parameter as defined below and in the incorporated documents.

“Monitoring parameter target” is the value of the monitoring parameter at which the food has finished cooking. It can be either a cooking score target or a temperature target.

“Conventional”—refers to a term or method designating which is known and commonly understood in the technology to which this invention relates. “Comparative examples” are examples obtained by or through the use of conventional devices and methods.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment and may apply to multiple embodiments. Furthermore, particular features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments.

The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for.”

DETAILED DESCRIPTION

Referring to FIG. 1, shown is a variable temperature oven 10 with programmable setpoint controller 11 which operates to control temperature in enclosure 12 according to a variable temperature reference profile (shown here are reference profiles 13 a, 13 b, 13 c, for example) stored in memory 14. Each “variable temperature reference profile” (RP_(n)) defines a variable termed the “oven temperature setpoint”, which is varied as a function of time for the duration of cooking. The oven temperature setpoint is the targeted oven cooking temperature (T) at any time (t). To control temperature, the controller loads a setpoint temperature from memory, and acts on a digital thermostat 15 which senses an oven temperature at sensor 16 in the enclosed cooking area 12. The temperature of interest is the cooking temperature within the cooking area and the thermostat operates to turn on power (power supply, 17) to a heating element that operates on the enclosed cooking area in response to an undertemperature condition. In response to an overtemperature condition the power is turned off. Even though not commonly used for ovens, proportional controllers can be envisaged. PID heating protocols may also be employed if desired. After a suitable interval, the controller then loads another setpoint, continuing so that the oven temperature follows a digitally programmed curve.

An optional oven probe 19 is also shown. The probe may be used to monitor internal temperature of the food during cooking. The probe may also be used to calculate a cooking score representative of the thermal history of the cooking cycle. In an improvement of the basic functionality described here, the probe data is supplied to the microprocessor and may be used to modify the initial setpoint temperature profile during the cooking process, as will be described in more detail below.

Variable temperature reference profiles (RP_(n)) are usually stored in memory and have been designed to cook meat or other foods using a pre-established heating profile of oven temperature versus time that optimizes certain cooking parameters like, for example, doneness. Other parameters can be meat tenderness or texture of some bread-like products. The profiles may be stretched in the time or temperature domain according to likes selected by the user. A single profile (RP_(l)) or multiple profiles (RP_(n)) may be stored in memory. The processor is typically programmed to execute a reference temperature profile by reading time and temperature from a table in memory and adjusting it based on certain algorithms to meet the current cooking conditions as input by the user or based on data received from a temperature monitoring probe inserted in the food. The digital thermostat setpoint is updated at selected intervals so that the oven is heated according to the profile.

In order to adjust the oven temperature at small time intervals during cooking, heating is controlled automatically using a variable temperature regulator. At each cooking temperature adjustment moment, the temperature setting setpoint is transmitted from the processor to the circuitry that controls the heating regime according to an applied variable temperature profile as determined by the processor. A digital thermostat works by comparing the current oven temperature with the target temperature from the applied variable temperature profile at and activating or shutting off the heating element as required. The algorithm for controlling the temperature can be devised in many different ways and the appliances may have a finer or larger temperature control range which may be selected to suit the application.

A variable temperature cooking apparatus can be implemented in various types of cooking appliances. Conventional electric or gas thermostat-regulated ovens are the prime candidates, and also rotisseries. Infrared oven or other cooking devices are also conceived.

Variable temperature reference profiles can range from a simple linear variation or multiple step functions to more elaborate variation with variable slope which can incorporate, for example, abrupt temperature increases and decreases. It can be determined that a certain temperature profile reference gives better results with a particular type of food. In such a case, selecting a certain food category would implicitly select a certain variable temperature reference profile. In order to define the particular cooking conditions, cooking duration and starting and ending temperatures must be known. One way is to input them manually or chose the default values. Other ways may consist in entering the type of food and quantity and let the appliance automatically figure out the cooking parameters and modify the variable temperature reference profile to match them.

For some foods, the final temperature needs to be above certain levels prescribed by the USDA to reduce bacterial counts. This should be taken into consideration in designing the cooking profile and oven temperatures so that the final temperature is above a certain level at the center of the product for a few minutes at least.

Setpoint controller 11 is a microprocessor or microcontroller and may include supporting circuitry, volatile memory, non-volatile memory, and/or supporting firmware configured with program instructions. Networked distributed computational modules are also envisaged. Heating enclosure 12 is selected from cooking areas or oven chambers known in the art. In a broader sense, any heating configuration that can benefit from a variable temperature profile can be a candidate, including cooktop appliances.

Digital thermostat 15 operates as a conventional thermostat to power the heating (and/or cooling) element(s), but is configured so that the digital setpoint may be continuously varied during the cooking cycle under control of the setpoint controller, according to the applied variable temperature profile. A user interface is supplied for entering information that customizes the variable temperature reference profile selected by the user.

Additional programmable features may include a brief temperature boost at the end of the cycle for browning, crunchy skin, or seared appearance if desired. Other cooking methods prescribe a temperature boost at the beginning of cooking. These special surface treatments can be regarded as additions to the cooking profile presented herein. They can be applied by manually overriding the cooking temperature, editing existing temperature variable temperature reference profiles using dedicated entries, or can be readily incorporated in a temperature variable temperature reference profile.

FIG. 2 is a block diagram depicting an embodiment of program logic for variable temperature cooking user interface. In this example, the user is invited to enter food type, quantity or cooking time, and to accept a default setpoint profile from memory. Alternatively, the user may enter a high temperature starting point, a low temperature end point, the cooking time, and select a different variable temperature reference profile. The use of a temperature probe for directly measuring food temperature is an optional choice in some appliances.

Similarly, it can be envisioned that a variable temperature oven can be used for cooking bakery products so that the center and outer areas can cook more uniformly prior to a browning phase, or a certain texture is obtained.

FIG. 3 illustrates a first embodiment of a control panel for a variable temperature cooking unit. Once the Variable Temperature cooking function is selected, the operator is asked to input a Starting temperature, a Final temperature and the Duration of cooking. This can be done by pressing one of the buttons on the right. A default value is displayed and the operator can increase or decrease the value using the UP and DOWN buttons until the preferred value is reached. Then he/she can continue setting the next values by pressing the appropriate buttons. An ENTER button may be provided.

Once the parameters are set, the appliance calculates an applied variable temperature profile that preserves the main beneficial characteristics of the variable temperature reference profile as explain before. Examples of functions that can be used for reference profiles are the median variation of Example 8 or the sigmoid variation of Example 6. A linear ramp from hot to warm can also be considered. The functions are not limited to the examples described here and an oven manufacturer can select a different curve which he considers to be more appropriate. A selection for a temperature profile to fit a type of food or a faster or slower cooking time can also be offered. A “USE PROBE” button to use the input from an internal temperature probe can be selected for appropriately equipped ovens.

FIG. 4 represents a second embodiment of a control panel for another variable temperature cooking unit with minimal required input parameters. First, CONSTANT or VARIABLE temperature is selected. For Variable temperature, an average temperature is entered by using the UP and DOWN buttons. The unit will automatically determine the maximum and minimum temperatures based on specifications coded in the heating algorithm. For example, for cooking pork the average temperature can be set to the normal cooking temperature of 350° F. The unit will then determine the maximum and minimum temperature by adding and subtracting certain values, for example, adding 40° F. and subtracting 40° F. for a 390° F. starting temperature and a 310° F. final temperature. An estimated cooking time (COOKING DURATION) is entered next. Once this is done, the unit will determine a temperature profile and the cooking can start.

In case the cooking time was not accurately estimated, the cooking time can be extended. A button functionality can be provided for this. The final temperature setting should provide enough heat for the cooking to continue. For flexibility, an override control may be provided so that the temperature or time can be manually reset during the cooking cycle.

Other methods of inputting the user parameters can be envisaged, such as inputting a descriptor from a list of preprogrammed options or scanning a barcode or QR code that can accompany a recipe, or by reading from a magnetic medium or strip. The oven can also be accessible over a wireless network or have a network adaptor for receiving instructions over an internet link such that variable temperature cooking instructions can be downloaded. Oven functionality can even be monitored in real time over the internet. The possibilities are numerous and input and remote monitoring technologies will evolve over time. Basic parameters such as cooking duration, starting and ending temperatures, or even the entire variable temperature reference profile can be entered using these modalities.

Doneness Determination

The main cooking characteristic for the determination of a variable temperature profile is, in this presentation, through-the-thickness doneness uniformity. Other criteria that can affect a variable temperature profile as mentioned beforehand are by no means excluded. This is especially emphasized by the fact the user is given the possibility of defining a temperature profile of his or her choosing. As part of the process for optimizing the temperature profile to improve through-the-thickness doneness, the following describes how doneness is determined.

Doneness and cooking score are closely related. Knowing one means knowing the other one. It is much easier and precise to determine the cooking score using a probe inserted into the food for monitoring the internal temperature during cooking than to determine doneness. This way doneness can be known at each moment at different measurement locations while determining doneness by tasting would mean interrupting the cooking process. It will also be prone to subjective variations in taste evaluation.

The relations used in this invention for calculating the cooking score are given below. More details are presented in US Pat. Publ. No. 2012/0100269, which is co-owned.

The cooking rate was calculated as:

CR(T)=Ae ^(−E) ^(a) ^(/RT)  (Eq. 1)

where T is the absolute temperature (° K), R is the gas constant, and E_(a) is an activation energy. The E_(a)/R was taken as 4,000, which is appropriate for pork which is used in the current experiments. Proportionality constant A=2.008×10⁵. For other foods, other cooking rate functions may be used.

The cooking score (CS) is obtained by integrating the cooking rate over time t. At time t₁ the cooking score is given by

CS(t ₁)=∫_(t) ₀ ^(t) ¹ CR(T)dt  (Eq. 2)

where t₀ as the initial time when cooking was started.

The cooking score will continuously increase with time at a rate that has strong temperature dependence. The higher the temperature, the faster the cooking score increases.

Informatively, for the current examples, a cooking score of about CSU=110 is the approximate lower limit of doneness.

Using this method, the doneness at different locations was calculated from the temperature history of the food. A history of temperature over cooking time is all that is needed to calculate cooking score. Then to determine the merits of different temperature profiles for uniform through-the-thickness cooking, the cooking score at the core of the food is compared with the cooking score near the top and bottom outer surfaces. Optimal results are achieved when the “Evenness Ratio” for the outer food layer versus the core approaches 1.0.

Variable temperature reference profiles can generally be any continuous function of time having a smoothly varying setpoint. A non-exhaustive classification can be made as follows:

-   -   constant temperature;     -   two step or multistep temperature profiles;     -   continuously increasing functions;     -   continuously decreasing functions; or a     -   any combination of the above, including multipeak functions.

FIG. 5 presents some of the profiles that have been used for evaluation of the invention. Shown are two sigmoid curves (21, 22), a parabolic curve (23), a median curve (24) averaging curves 22 and 23, and a natural cooling curve (25) as will be discussed in more detail with respect to the variable cooking temperature cycles of the Examples. Natural cooling curve 25 is insufficient for most cooking purposes, thus the cooking profiles 21, 22, 23 and 24 represent digitally controlled heating profiles.

In the following experimental work, the operation of the present invention will be described in further detail with reference to examples of constant temperature, two-step profiles, multipeak functions, and continuously decreasing functions. However, it should be understood that the present invention is not restricted to the specifics of the Examples, but is rather defined by the claims.

Experiments have been performed to evaluate these patterns and the results are compared in terms of their merits of achieving a more uniform though-the-thickness doneness. For this, the temperature readings at outer and center locations are converted into cooking scores in order to estimate doneness. It will be shown that the continuously decreasing temperature profiles perform better than constant or two step temperature profiles and, among those, the sigmoid type provide the best results, followed closely by essentially linear decreasing temperature profiles.

Conventional Cooking Processes

Conventional cooking experiments characterized by constant temperature and two step temperature profiles were performed to establish benchmark comparative examples for other temperature profiles.

Example No. 1

an uncooked, uncured pork loin weighing about 1.2 pounds was cooked using a constant temperature profile and cooking score was calculated as previously described by Equations (1) and (2). The oven temperature was set at 350° F. The temperatures at the top, center, and base were recorded during the cooking process using continuous monitoring temperature probes. Results are presented in FIGS. 6A and 6B.

After 120 minutes, the center of the piece had a cooking score CS=115. This value indicates a rare-to-medium doneness. However, the outer skin at 120 min had a cooking score CS=196, meaning this layer is overcooked. The underside had a CS of 259, an undesirable outcome.

Example No. 2

a similar amount of pork as in Example No. 1 was heated at a constant oven temperature of 300° F. After 132 minutes, the cooking score at the center was CS=115. The cooking score at the top and the base turned out to be practically the same at 187 due mainly to the slow cooking process. The temperature and cooking score variation are presented in FIGS. 7A to 7B.

Example No. 3

a two-step heating profile starting at 375° F. for 20 minutes and continued at 310° F. is presented in FIGS. 8A thru 8C. The cooking score at the center after 120 minutes was 124, at the top 177, and at the base 242. Both center and top Evenness Ratios are less than those of the two constant temperature profiles shown in FIGS. 6 and 7.

It has been noticed that the bottom temperature (and hence cooking rate) is harder to control since it is in contact with the cooking vessel and may depend strongly on the position of the vessel in the oven. Still, even for the bottom location, a constantly decreasing variable temperature profile as described below showed an improvement over the above methods.

Variable Temperature Cooking Processes

One category of temperature variation is an impulse or “sawtooth” heating profile where the temperature varies in a seesaw fashion. The oven is first brought to a high temperature and then let to cool off naturally due to heat losses (FIG. 5, n. 25) until a prescribed minimum temperature is reached. At this point the heating starts again until a prescribed maximum temperature is reached. The process is repeated until the food reaches doneness. One could be tempted to think that allowing the heat accumulated in the outer areas to be transferred to the center during break provided by the cooling period and only then start reheating could lead to a more uniform temperature distribution and therefore a more uniform doneness. The following experiments test this assumption.

Example No. 4

an uncooked, uncured pork loin weighing about 1.2 pounds was cooked using an impulse heating profile. The oven was alternatively heated to 310° F. and then let to cool passively to 200° F. The results are presented in FIGS. 9A thru 9C.

The results show the outer (top and bottom) areas undergoing temperature humps that follow the oven temperature patterns (FIG. 9A). During the peaks, the outer temperature increases relative to the center temperature. Once the heat is cut and the oven starts cooling, the outer temperature tends to converge toward the center temperature. The effects of the oven temperature peaks are less apparent in the center temperature variation. Even though the two temperatures do come close at times, it is difficult to estimate the overall effect just by looking at the temperature curves. The final doneness is best judged considering the cooking score.

It took 140 minutes to achieve a center cooking score of 115 CSU while the top area achieved 162 CSU. At an Evenness Ratio or 1.38, this is the most uniform through-the-thickness doneness achieved so far. This is in a large part due to low maximum oven temperature and the resulting slow cooking process.

Example No. 5

a similar impulse heating experiment that uses a higher maximum temperature is presented in FIGS. 10A thru 10C. Pork loin weighing about 1.2 pounds was cooked in an oven alternate cycles of heating to 400° F. followed by natural cooling to 200° F.

After 104 minutes, the cooking score at the center was a low 84 CSU and at the top was 147 CSU for an Evenness Ratio or ratio of 1.75. As before, the effect of the oven temperature humps are mostly seen in the outer area temperature variation with the center being very slightly affected. The Evenness Ratio is of the order of magnitude found for the conventional higher constant temperature heating.

Example Nos. 4 and 5 show that impulse heating cooking does not result in an improvement of doneness through-the-thickness uniformity. There is also much more to learn from these examples. Increasing oven temperature heats the outer areas faster than the center area moving the outer temperature further apart from the center temperature. The effect is that the cooking scores diverge. Decreasing the oven temperature brings the outer temperature closer to the center temperature making the cooking scores converge. Since most of the cooking takes place at elevated temperature it is not good to have temperature increases in this area. Since the temperature needs to be increased anyway, it is therefore best to have that happen at lower temperatures. At higher temperatures the best performance would come from a decreasing oven temperature profile which will tend to equalize the temperatures throughout the food.

The rate to which the temperature decreases is also important. To accelerate heating and to create enough initial difference between the outer and center temperatures one can hold the higher temperature longer in the early stages. The temperature can also be decreased more rapidly in the later stages to make the temperatures converge more rapidly at higher temperature. This can be done using a concave down (concave) parabolic temperature variation for the first part followed by a concave up (convex) parabola in the second part resulting in a sigmoid temperature profile. These projections will be verified by the following experiments.

Continuously Decreasing Temperature Setpoint Processes

As seen above, in order to eliminate top and bottom hotspots, recurring oven temperature increases are generally best avoided. In the following experiments, the temperature is made to decrease continuously. A number of such profiles were depicted in FIG. 5.

Example No. 6

an uncooked, uncured pork loin weighing about 1.2 pounds was cooked using the sigmoid variable temperature cooking profile of FIG. 5 (n. 21). Starting from an initial value of 380° F., the oven temperature setting was progressively decreased to 305° F. by manually adjusting the thermostat to follow the prescribed curve, as shown in FIG. 11A. The temperatures at the top, center, and base were recorded during the cooking process using continuous monitoring temperature probes (FIG. 11B). Cooking score for each layer was calculated as described above (FIG. 11C). After 120 minutes, the cooking score at the center was 113 CSU, at top 144 CSU and at the base 225 CSU. Due to the continuous contact with the hot wall or vessel, the temperature at the base stays high as it cannot be dissipated convectively.

The top Evenness Ratio was 1.27, significantly lower than the constant heating profile of experiment No. 1 while the cooking time and doneness level where practically the same.

The plots show that at high oven temperatures, the center temperature approaches the top temperature and even crosses it. This is different than either two-step or impulse heating and is an indication that more even doneness is to be achieved. The phenomenon is remarkable and its effect has only been seen for continuously decreasing oven temperatures. A transpiration phenomenon has been observed at the surface of the meat and one can speculate that moisture from the center is pushed toward the surface due to a pressure buildup and capillarity effects. Evaporation on the surface would then contribute to reduce or even invert the rate at which the top surface temperature raises.

Example No. 7

an uncooked, uncured pork loin weighing about 1.2 pounds was cooked using a slightly different sigmoid temperature profile (FIG. 5, (22) starting from a lower initial temperature of 370° F. and ending at 295° F. The raw data from each temperature probe and the resulting cooking score are presented in FIGS. 12A-C. After 125 minutes cooking score at center was slightly higher than previously at 119, at the top was 138, and 201 CSU at the base. Top Evenness Ratio is the lowest at 116% with only a slight increase in total cooking time. The base Evenness Ratio is also lower at 169 CSU.

Example No. 8

an uncooked, uncured pork loin weighing about 1.2 pounds was cooked using a “median” temperature profile (FIG. 5, n. 24) obtained as an average between the sigmoid profile of Example No. 7 (FIG. 5, n. 22) and a convex (concave up) parabola (FIG. 5, n. 23). The oven temperature profile, identified here as the “median temperature profile,” starts from 370° F. and progressively decreases down to 300° F. Top Evenness Ratio was very close to the previous experiment at 1.18 and so was the base Evenness Ratio of 1.68. It is interesting to note that the median profile is very close to a linearly decreasing temperature profile. The raw data from each temperature probe and the resulting cooking score are plotted in FIGS. 13A-C for the median temperature profile of Example No. 8.

FIG. 14 tabulates cooking data from the Conventional Cooking and Variable Temperature Cooking Examples. In Example No. 6, the top layer had a cooking score of 144 and the center 113 CSU, an Evenness Ratio of about 1.27. As shown in Example No. 1, an Evenness Ratio of 1.70 was obtained by constant temperature cooking at 350° F. For Example No. 7, cooking score in the top layer CS=138 CSU; in the center CS=119 CSU, an Evenness Ratio of 1.16, showing an even more significant improvement in evenness of cooking.

In Example No. 8, a median profile is shown to result in cooking scores for the top layer (141 CSU) and for the center (120 CSU) that are relatively uniform, having an Evenness Ratio of only 1.18 top to center, also a very good value.

It can be seen that a variable temperature cooking profile as described in examples 6 thru 8 provides a significant benefit in the form of improved evenness of cooking between the center doneness and the top surface than comparative examples at constant temperature. The Sigmoid temperature curve of Example No. 7 produced the most uniform cooking, followed closely by Example No. 8. Cooking duration is another important parameter. This is especially true since variable temperature cooking attempts to achieve results that were previously possible only with slow cooking methods in normal cooking time, essentially the benefits of slow cooking without the “slow”.

Example Nos. 4 and 5 where heating was followed by natural cooling in an attempt to allow the center to catch up with the skin temperature, did not provide very good results. Evenness Ratios were similar to the constant temperature examples. Even though they did not produce any visible improvements, these experiments offered important insight into the food doneness reaction to temperature variations during cooking. Cooking score was helpful in making these assessments. It has been determined that raising the temperature during cooking negatively affects doneness uniformity while a decreasing temperature helps.

Variable temperature cooking was also a significant improvement over a two-step heating adjustment such as described in Comparative Example Nos. 5 and 6. The two-step method, which can be regarded as a partial variable temperature variation, resulted in an Evenness Ratios of 1.43 which is slightly higher than the average value between constant temperature and the fully variable temperature variation of Example Nos. 6 thru 8.

The experiments show that a variable temperature characterized by a smooth temperature decrease provides a more uniform doneness distribution throughout the volume of the food than constant or one-step temperature profiles. It is remarkable that, at higher food temperatures, as the oven temperature decreases, the outer skin temperature rises at a lower rate or even decreases while the center temperature keeps rising.

These results show that an optimal variable temperature reference profile can bring significant improvement compared to current methods. Basing oven temperature solely on food temperature instant readings is too limiting as the final state of the food, which is a function of the entire cooking temperature history, not just the state at a particular moment in time.

An optimum variable temperature reference profile can be constructed in advance by experimentation. The cooking result described here is uniform through-the-thickness doneness, but temperature profiles can target different cooking results as already mentioned. The present invention deals with how a variable temperature cooking profile developed in laboratory conditions for certain conditions can be applied to real cooking situations. Using it does not necessarily need an internal temperature probe. Being able to be independent of such a probe can be an advantage for manufacturers, who can build a more cost-effective product, and also for consumers, who do not have to put up with handling the probe by inserting in the food, cleaning it after use, and storing it afterwards.

Adapting the Reference Temperature Profile to Actual Conditions

The determination of an optimum variable temperature reference profile is usually done under laboratory conditions, and may require many trial-and-error experiments. The result of these experiments is a variable temperature reference profile characterized by a starting target setpoint temperature, an ending target setpoint temperature, a cooking duration (CD), as well as the general trend shape of temperature profile given by the paired datapoints for time and temperature (t,T) along the entire temperature variation. However, for a practical application in which the user may decide to change the start and the ending temperatures, or in which the food quantity, food type, and/or desired level of doneness require a different cooking duration, the curve derived in the lab is not typically usable without adaptation. The variable temperature reference profile may be adapted by user-entered variables like user-adjusted cooking duration, user-adjusted start temperature, or user-adjusted end temperature. Typically a mathematic transformation is used such that for any table of paired datapoints (t,T), a function can be written that transforms the table into paired datapoints (t*,T*). For example, a proportionality relationship may be used to rescale the initial profile for a longer cooking time or a higher starting target temperature setpoint, essentially rescaling one or both axes. Thus the initial variable temperature reference profile is “stretched”, “compressed,” or, in the most general sense, “mapped” for each setpoint data pair used by the microprocessor to control the oven temperature. The resulting temperature profile defines the applied variable temperature profile which is used to supply the temperature setpoints during an actual cooking session.

For rescaling in the time domain, such as to increase or decrease cooking time, the variable temperature reference profile is stretched or compressed in the t-axis by defining a new time coordinate t′ given by Eq. 3. A time transformation function can be written as:

$\begin{matrix} {t^{\prime} = {{t*\frac{t_{2} - t_{0}}{t_{1} - t_{0}}} - {t_{0}*\frac{t_{2} - t_{1}}{t_{1} - t_{0}}}}} & (3) \end{matrix}$

where t₀ is the timepoint where the stretching begins, t₁ is the end time for the stretching on the initial temperature profile, t₂ is the end time after the stretching. Therefore, (t₂−t₁) is the amount by which the temperature profile is to be stretched and (t₁−t₀) is the interval to be stretched.

FIG. 15 illustrates a time transformation process graphically. Two transformations are shown. In a first transformation, the variable temperature reference profile 150 is extended proportionately from 120 min to 180 min according to Eq. 3. The modified cooking profile is shown as a smooth dashed line 151.

In a second example, curve 152 illustrates a transformation process that shifts the reference curve to the right by adding a constant temperature “soak” interval of 1 hr and then resuming a sigmoidal temperature decay that terminates at 180 min. Basically, the reference curve was broken in the middle where a constant temperature segment was added. Even though the performance would probably not be as good as an optimum temperature profile for doneness uniformity, the modified profile is given to show the variety of stretching techniques that can be used.

A temperature transformation function is given by Eq. 4:

$\begin{matrix} {{T^{''}(t)} = {{\left( {1 + \frac{{\Delta \; T_{2}} - {\Delta \; T_{1}}}{T_{2} - T_{1}}} \right)*{T(t)}} + {T_{2}\frac{{\Delta \; T_{2}} - {\Delta \; T_{1}}}{T_{2} - T_{1}}} + {\Delta \; T_{2}}}} & (4) \end{matrix}$

where T″(t) is the new temperature profile after stretching, T₂ and T₁ are the temperature at the beginning and the end of the temperature stretch interval, and ΔT₂ and ΔT₁ are the amount of stretch at these points.

FIG. 16 illustrates a linear temperature rescaling using Eq. 4. The start temperature setpoint is increased from 380 on the reference curve (160) to a higher temperature on the modified curve (161, dashed line), and the end target temperature is dropped. Each remaining datapair is modified so that the curve is rescaled on the T-axis proportionately.

Time and temperature transformations can be combined in a single function when the variable temperature reference profile is to be rescaled on both axes; the mapping functions are not limited to linear rescaling processes—more complex mapping operations can be employed. Mapping can involve, for example, developing two reference optimum curves for different conditions and then develop a mapping function that morphs one curve onto the other. Cooking under conditions between the two curves can then be interpolated and conditions outside the reference curves can then be extrapolated. There might also be cases when it might be desirable to bias the mapping function in a certain direction or to use different transformations for different portions of the profile. One example is when a searing portion is incorporated in the temperature profile. In this case the cooking profile may be modified in part by one operation and a searing portion may be stretched by a different operation.

Using a Temperature Monitoring Probe

Some of the more recent oven models are equipped with a temperature monitoring probe that can be inserted in the food. The probe provides continuous, instantaneous monitoring of the internal temperature of the food. As conventionally used, the probe signal is used to stop the cooking process and trigger an alert when the internal temperature reaches a certain value. Alternatively, as described in US Pat. Publ. No. 2012/0100269, probe data can be used to calculate a cumulative parameter, called Cooking Score, that takes into account the entire temperature history and provides a better criteria for achieving the desired doneness. Thus in a variation on conventional teachings, a probe (FIG. 1, n. 19) can be used to discontinue cooking when the cooking score reaches a certain value.

In an improvement to the variable temperature cooking appliances of the invention, so as to fully exploit their benefits when supplied with a probe, the probe data may be used to calculate adjustments on the fly to the setpoint temperature profile in memory.

FIG. 17 shows a cooking score curve (170) recorded during a cooking session. It is desirable to be able to estimate the duration of cooking time required to achieve a targeted cooking score (171), which again, is an indication of doneness and is calculated from probe temperature data. The duration of cooking at any point can be estimated by the tangent to the curve at that point and its intersection with the target cooking score line, in this case 120 CSU. For lower cooking scores, as shown during the first 50 minutes of cooking in this example, the tangent line (172, dashed line) at point A strongly overpredicts cooking time. However, predictions become more accurate as the cooking score increases. For example, 45 minutes before the target score is reached the prediction is within 9.23 minutes, 25 minutes before the end is 2.17 minutes and 10 minutes before the end accuracy is just 24 seconds. It can be seen at point B that the intercept between the tangent line 173 and the horizontal target line 171 is well defined, which facilitates good numerical behavior.

Cooking score predictions are substantially better than raw temperature data from the probe, as shown in FIG. 18, where the same cooking session is modeled using the raw probe data 180. Unlike the tangent lines drawn to the cooking score curve of the previous figure, here the tangent lines tend to become parallel with the target temperature line 181, which makes the crossing exceedingly sensitive to system errors and, if internal temperature flattens out or even starts to drop slightly for a variable temperature profile, the crossing may not even be defined, resulting in a failure to detect an endpoint and possible overcooking. Accuracy at high cooking scores or temperatures is most important since this is where most of the cooking occurs. At point A, where temperature is ramping up, the tangent line 182 is subject to a large time error (Δt_(A)), and at point B, where temperature is peaking, the error is even bigger and in the opposite direction (Δt_(B)), now underestimating cooking duration. At point C, the error (Δt_(C)) is relatively small, but very small variations in the intercept with the target temperature have large impacts on doneness since doneness is increasing sharply at this point (see FIG. 17 for an estimation of the cooking rate).

In contrast, in FIG. 17, at point A, the error (Δt_(A)) is large, but by point B, the error (Δt_(B)) is converging on a numerical solution, and at point C, the error (Δt_(C)) is so small that it cannot be readily graphed. By quantitatively assessing the change in the tangent line slope as a function of time, it is possible to predict the correct cooking duration in advance. Thus, as would not readily have been predicted, the cooking score obtained with a probe offers a powerful solution to predicting both doneness and cooking duration when used in a variable temperature appliance.

In a preferred embodiment, the following cooking score algorithm can be used to incorporate feedback with a continuous temperature monitoring system into a variable temperature cooking appliance of the invention. The algorithm is based on cooking score monitoring. The user executes the following steps:

a) select cooking parameters (see FIGS. 3 and 4) to define the starting and end temperatures (T₂ and T₁), the selected reference temperature profile, and an initial cooking duration CD₀. For simplification, it will be assumed that the user defined starting target setpoint and end temperatures are unchanged from the reference temperature profile. If the user makes a change, a temperature transformation can be performed to refit the profile and generate modified setpoint datapairs; b) select “probe correction” modality and enters or selects target cooking score, in this mode the probe data will be used to update the setpoint and cooking profile at at least one timepoint during the cooking cycle; c) insert a probe (19) into the food and connects it to oven if needed; and d) at one or more discrete moments in time t_(i), the oven-based controller executes the following steps: 1. calculate cooking score at the current time t_(i) (CS_(i)) using Eq. (2) 2. calculate an estimated cooking duration at the current time t_(i) (CD_(i)):

$\begin{matrix} {{CD}_{i} = \frac{\left( {{CS}_{t} - {CS}_{i\;}} \right)}{\frac{{CS}}{t}\left( {t = t_{i}} \right)}} & (5) \end{matrix}$

where

$\frac{{CS}}{t}\left( {t = t_{i}} \right)$

is the derivative (i.e., tangent line) of the cooking score at current time t_(i) and CS_(t) is the target cooking score. 3. transform the variable temperature reference profile and determine the current probe-adjusted cooking duration (CD_(i)) using Eq. 3 as the mapping function. Considering the start time t₀ to be 0, the relation becomes

$\begin{matrix} {t^{\prime} = {t*\frac{{CD}_{i}}{{CD}_{0}}}} & (6) \end{matrix}$

Thus, at time t_(i), the cooking duration and temperature profile are updated based on the cooking score prediction, and with each recursion, it progressively becomes more accurate;

4. write the modified temperature profile in volatile memory, read the next setpoint temperature T_(i+1) at time (t_(i)+dt), where dt is the time of the next update; 5. heat oven to T_(i+1) according to the thermostat algorithm. 6. after the dt interval elapses, (t_(i)+dt) becomes t_(i), make a new temperature reading from the probe and update the new cooking score value CS_(i) and T_(i); 7. if CS_(i)≧CS_(t), then issue a notification to the user and stop the cooking session, and if CS_(i)<CS_(t), then steps 1 thru 6 are repeated until the target cooking score is achieved.

This method improves variable temperature cooking processes. If the initial cooking duration CD entered by the user is not accurate, then the variable temperature reference profile will have to be stretched or compressed to achieve the desired doneness. If this is not done, the food will be either undercooked or overcooked at the designated time. If undercooked, reheating and adding more time is not desirable; and can result in a late dinner service. If overcooked, the qualities of the food cannot be recovered.

A feedback loop involving measuring internal food temperature and calculating cooking score is used to accurately predict cooking duration in advance, and a countdown may be shown on the user interface if desired.

Examples were run in which the reference temperature profile 150 of FIG. 15 was considered in more detail. It was assumed that at each point the cooking score is given by the curve in FIG. 17. Even though the cooking score variation will be different for different temperature profiles, the assumption allow us to illustrate some characteristics of the method. Several scenarios are presented in FIG. 19. Curve 190 represents the oven temperature when the oven is programmed for non-probe based heating for a CD of 125 minutes. This is the “variable temperature reference profile” and represents a preferred temperature profile for a certain cooking duration CD. When cooking duration is not accurately known, a probe-assisted method may be used to incorporate the probe feedback calculation described above. Curve 191 is based on the cooking score algorithm described above, essentially as represented in FIG. 17. Because the cooking score overpredicts the cooking duration during the first part of cooking session, the oven temperature is higher during that part and must compensate by trying to converge sharply down onto curve 190 in the middle of the curve. This is likely to result in overcooking. One method to remedy this is to use the initial duration estimated by the user, i.e., a best guess. Curve 192 shows the results when the user overestimates the CD, entering 150 minutes. Here, any cooking duration determined by the algorithm that is higher than 150 minutes is replaced with the user estimate of 150 minutes. This results in a setpoint profile that more closely fits the variable temperature reference profile. Curve 193 shows the result when the user underestimates the CD, entering a guess of 100 minutes. Here, the cooking duration determined using the algorithm at time below 100 minutes is replaced with the user estimate of 100 minutes. Another method can be based on some algorithms to predict the cooking score derivatives and thus being able to come up with a more accurate cooking duration faster.

In summary, it is generally known that cooking cannot be accelerated by raising the oven temperature beyond certain practical limits or burning, starting on the skin, results. Conversely, cooking below a lower temperature limit results in more uniform cooking throughout the food, but takes a longer time, sometimes significantly longer. The “thermal decay” temperature profiles of the present invention make the duration of the cooking process comparable to a regular cooking with normally prescribed (relatively high) oven temperatures but with results comparable to slow cooking (uniformity of doneness and moisture content).

While there is provided here a full and enabling disclosure of the preferred embodiments of this invention, the invention is not limited to the exact construction, dimensional relationships, and operation shown and described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true spirit and scope of the invention. Such changes might involve alternative temperature profiles, materials, components, structural arrangements, sizes, shapes, forms, functions, operational features or the like, for example. Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is defined by the appended claims.

INCORPORATION BY REFERENCE

All of the US patents, US patent applications, patent publications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and related filings are incorporated herein by reference in their entirety. 

1. An apparatus for cooking, which comprises a) a cooking area for receiving a food item to be cooked; b) a processor and digital memory, said processor capable of reading data pertaining to a variable temperature reference profile, said variable temperature reference profile comprising a table of setpoint target temperatures over a cooking duration, and supplying setpoint target temperatures to a temperature controller during said cooking duration according to said variable temperature reference profile, said setpoint target temperatures defining an applied variable temperature profile; c) wherein said temperature controller is linked to said processor, said temperature controller for sensing a temperature within said cooking area and for controlling a heating member operative on said cooking area so that said temperature is driven according to said temperature setpoints of said applied variable temperature profile.
 2. The apparatus of claim 1, further comprising a user interface, wherein said user interface is enabled for user-mediated modification of a existing variable temperature reference profile including a user-adjusted cooking duration, user-adjusted start temperature, and user-adjusted end temperature.
 3. The apparatus of claim 1, further comprising a user interface, wherein said control surface is enabled for user-mediated input of a variable temperature reference profile.
 4. The apparatus of claim 2, wherein said processor is programmed for mapping time-temperature datapairs (t, T) of said variable temperature reference profile to time-temperature datapairs (t*, T*) of said applied variable temperature profile as defined by said user-adjusted cooking duration, said user-adjusted start temperature, and said end user-adjusted temperature as modified by said user.
 5. The apparatus of claim 1, wherein said variable temperature reference profile comprises time and temperature datapairs defining a variable temperature function characterized by a smoothly decreasing temperature between a higher temperature setpoint and a lower temperature setpoint.
 6. The apparatus of claim 5, wherein said curve is selected from a descending sigmoid curve, a descending parabolic curve, a descending median curve, or a descending linear ramp.
 7. The apparatus of claim 2, wherein said user interface is configured for selecting a maximum cooking temperature, a minimum cooking temperature, an average cooking temperature, a food type, a food weight, a food thickness, a doneness target; or a machine default condition.
 8. The apparatus of claim 2, where the variable temperature reference profile can be selected by the user from a library of variable temperature reference profiles.
 9. The apparatus of claim 1, further comprising an insertable probe or sensor and probe temperature control circuit configured for continuously monitoring and relaying internal food temperature data to said processor in real time.
 10. The apparatus of claim 9, further comprising a user interface configured for actuating said probe temperature control circuit, for selecting a monitoring parameter, and for entering a monitoring parameter target indicative of completion of cooking.
 11. The apparatus of claim 10, wherein said processor comprises instructions for mapping time-temperature datapairs (t, T) of said variable temperature reference profile onto time-temperature datapairs (t*, T*) of an applied variable temperature profile according to input temperature data received from said probe during said cooking session.
 12. The apparatus of claim 11, wherein said instructions comprise steps for calculating a rate of change of said monitoring parameter over a time interval and extrapolating from the derivative an estimated probe-adjusted cooking duration required to obtain said monitoring parameter target, wherein said monitoring parameter target is indicative of completion of cooking.
 13. The apparatus of claim 12, wherein said monitoring parameter target is a cooking score indicative of doneness.
 14. The apparatus of claim 12, further comprising a display for displaying a countdown based on estimated time to completion of cooking, wherein said countdown is periodically updated.
 15. The apparatus of claim 1, wherein said processor has instructions for turning down said heating member when time to completion of cooking is zero.
 16. The apparatus of claim 13, wherein said processor has instructions for turning down said heating member when said cooking score is reached. 